Generic ground milling machines, such as road milling machines, recyclers, stabilizers and surface miners, are used in road and path construction or in the surface mining of natural resources. The working tool of these machines is a milling drum, which is rotatably mounted in a milling drum box and which can be driven by the power unit of the ground milling machine by means of a transmission. During working operation of the ground milling machine, the ground milling machine is moved over the ground by means of travelling devices, while the rotating milling drum mills off ground material. The milling drum box encloses the milling drum like a cover opened towards the ground and, on the one hand, prevents loosened milled material from being thrown out of the milling drum box, and, on the other hand, either directs the milled material to a discharge conveyor belt by means of which the milled material can be transferred to a transport vehicle and carted off, or ensures a defined depositing of the milled material on the ground.
The shape of the milling drum box is adapted to the milling drum. In order to be able to use, for example, milling drums of different widths and/or equipped in a different fashion, which are adapted to a given particular operational situation, together with the same ground milling machine, it is known to remove the entire milling drum box from the ground milling machine and to mount another milling drum box, which is equipped with the milling drum adapted to the particular situation, on the ground milling machine. As the milling drum boxes and corresponding milling drums are large and very heavy machine components, mounting them on or removing them from the ground milling machine can be a complicated and sometimes time-consuming process. Consequently, special exchangeable milling drum boxes have been developed, which allow a particularly quick and easy dismounting and mounting on the ground milling machine. These types of ground milling machines with special exchangeable milling drum boxes are described, for example, in the applications DE 10 2014 011 856, DE 10 2015 016 620, DE 10 2015 016 671, DE 10 2015 016 672, DE 10 2015 016 678, and DE 10 2015 016 679. In order to emphasize the modular design of a ground milling machine having an exchangeable milling drum box, reference will also be made below to a machine part of the ground milling machine and an exchangeable milling drum box. In this connection, the machine part of the ground milling machine designates all parts of the ground milling machine that are not part of the exchangeable milling drum box and which remain on the ground milling machine after dismounting the exchangeable milling drum box.
Thus, in addition to the components pertaining to the exchangeable milling drum box itself, the exchangeable milling drum box normally comprises a milling drum and parts of the drive train. For example, an exchangeable milling drum box frequently comprises a transmission, normally in the form of a planetary gear, which, on its drive side, can be connected to a drive train of the ground milling machine, for example, via a belt or chain gear or a hydraulic connection, and, on its output side, drives the milling drum. This transmission usually has a lubrication device, the function of which is to supply the transmission with lubricant. As the lubricant heats up during operation of the ground milling machine, it must be cooled. For this purpose, the lubricant is normally conveyed from the milling drum box to a heat exchanger/cooler on the machine part of the ground milling machine. This heat exchanger/cooler is connected, for example, to a hydraulic fluid cooling circuit or a cooling water circuit of the machine part of the ground milling machine or is passed through a cooling fan airstream. In addition to cooling the lubricant, the latter can advantageously also be heated after a cold start of the machine by means of the heat exchanger, whereby the viscosity of the lubricant is reduced faster after starting the ground milling machine, which reduces wear on the gear parts and, for example, on a lubricant pump. The problem with this design for cooling and/or heating lubricant when using exchangeable milling drum boxes is that there is a relatively large amount of lubricant in those parts of the lubricant circuit that are arranged on the machine part of the ground milling machine. If the ground milling machine is turned off, a portion of this lubricant runs from the machine part back into the transmission of the milling drum, i.e., into the exchangeable milling drum box. Thus, the lubricant is distributed over the machine part and the exchangeable milling drum box. The amount of lubricant removed from the ground milling machine with an exchangeable milling drum box thus varies depending on how long the ground milling machine has already been shut off prior to removal and, consequently, how much time the lubricant has had to flow back into the transmission. Thus, in particular, where multiple exchangeable milling drum boxes are used, excessive amounts of lubricant can either be stepwise removed or supplied to the ground milling machine, which leads to problems with respect to lubricant balance. Current developments in exchangeable milling drum boxes thus result in the described challenges regarding the lubricant balance in the ground milling machine.
The object of the present invention, therefore, is to overcome the described problems regarding the lubricant balance, in particular ground milling machines having exchangeable milling drum boxes.